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    小心MySQL的隐式类型转换陷阱
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    小心MySQL的隐式类型转换陷阱 | 数盟社区
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         <a href="http://dataunion.org/24319.html">
          小心MySQL的隐式类型转换陷阱
         </a>
        </h1>
        <address class="msccaddress ">
         <em>
          373 次阅读 -
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          编程语言
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       <div class="article fmt article__content" data-id="1190000005136982" data-license="cc">
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         1. 隐式类型转换实例
        </h2>
        <p>
         今天生产库上突然出现MySQL线程数告警，IOPS很高，实例会话里面出现许多类似下面的sql：(修改了相关字段和值)
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
        <div class="crayon-syntax crayon-theme-classic crayon-font-monaco crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover" id="crayon-576869a364200165427323" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
         <div class="crayon-toolbar" data-settings=" mouseover overlay hide delay" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
          <span class="crayon-title">
          </span>
          <div class="crayon-tools" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
           <div class="crayon-button crayon-nums-button" title="切换是否显示行编号">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-plain-button" title="纯文本显示代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-wrap-button" title="切换自动换行">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-expand-button" title="点击展开代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-copy-button" title="复制代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-popup-button" title="在新窗口中显示代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <span class="crayon-language">
            Java
           </span>
          </div>
         </div>
         <div class="crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
         </div>
         <div class="crayon-plain-wrap">
          <textarea class="crayon-plain print-no" data-settings="dblclick" readonly="" style="-moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; font-size: 12px !important; line-height: 15px !important;" wrap="soft">
           SELECT f_col3_id,f_qq1_id FROM d_dbname.t_tb1 WHERE f_col1_id=1226391 and f_col2_id=1244378 and 
f_qq1_id in (12345,23456,34567,45678,56789,67890,78901,89012,90123,901231,901232,901233)
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a364200165427323-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364200165427323-2">
                2
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a364200165427323-1">
                <span class="crayon-e">
                 SELECT
                </span>
                <span class="crayon-v">
                 f_col3_id
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-e">
                 FROM
                </span>
                <span class="crayon-v">
                 d_dbname
                </span>
                <span class="crayon-sy">
                 .
                </span>
                <span class="crayon-e">
                 t_tb1
                </span>
                <span class="crayon-e">
                 WHERE
                </span>
                <span class="crayon-v">
                 f_col1_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1226391
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 f_col2_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1244378
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364200165427323-2">
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 12345
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 23456
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 34567
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 45678
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 56789
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 67890
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 78901
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 89012
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 90123
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901231
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901232
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901233
                </span>
                <span class="crayon-sy">
                 )
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0021 seconds] -->
        <p>
        </p>
        <p>
         用 explain 看了下扫描行数和索引选择情况：
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
        <div class="crayon-syntax crayon-theme-classic crayon-font-monaco crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover" id="crayon-576869a36420d736885678" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
         <div class="crayon-toolbar" data-settings=" mouseover overlay hide delay" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
          <span class="crayon-title">
          </span>
          <div class="crayon-tools" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
           <div class="crayon-button crayon-nums-button" title="切换是否显示行编号">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-plain-button" title="纯文本显示代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-wrap-button" title="切换自动换行">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-expand-button" title="点击展开代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-copy-button" title="复制代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-popup-button" title="在新窗口中显示代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <span class="crayon-language">
            Java
           </span>
          </div>
         </div>
         <div class="crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
         </div>
         <div class="crayon-plain-wrap">
          <textarea class="crayon-plain print-no" data-settings="dblclick" readonly="" style="-moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; font-size: 12px !important; line-height: 15px !important;" wrap="soft">
           mysql&gt;explain SELECT f_col3_id,f_qq1_id FROM d_dbname.t_tb1 WHERE f_col1_id=1226391 
and f_col2_id=1244378 and f_qq1_id in (12345,23456,34567,45678,56789,67890,78901,89012,90123,901231,901232,901233);
+------+---------------+---------+--------+--------------------------------+---------------+------------+--------+--------+------------------------------------+
| id   | select_type   | table   | type   | possible_keys                  | key           | key_len    | ref    | rows   | Extra                              |
+------+---------------+---------+--------+--------------------------------+---------------+------------+--------+--------+------------------------------------+
| 1    | SIMPLE        | t_tb1   | ref    | uid_type_frid,idx_corpid_qq1id | uid_type_frid | 8          | const  | 1386   | Using index condition; Using where |
+------+---------------+---------+--------+--------------------------------+---------------+------------+--------+--------+------------------------------------+
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a36420d736885678-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36420d736885678-2">
                2
               </div>
               <div class="crayon-num" data-line="crayon-576869a36420d736885678-3">
                3
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36420d736885678-4">
                4
               </div>
               <div class="crayon-num" data-line="crayon-576869a36420d736885678-5">
                5
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36420d736885678-6">
                6
               </div>
               <div class="crayon-num" data-line="crayon-576869a36420d736885678-7">
                7
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a36420d736885678-1">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-e">
                 explain
                </span>
                <span class="crayon-e">
                 SELECT
                </span>
                <span class="crayon-v">
                 f_col3_id
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-e">
                 FROM
                </span>
                <span class="crayon-v">
                 d_dbname
                </span>
                <span class="crayon-sy">
                 .
                </span>
                <span class="crayon-e">
                 t_tb1
                </span>
                <span class="crayon-e">
                 WHERE
                </span>
                <span class="crayon-v">
                 f_col1_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1226391
                </span>
                <span class="crayon-h">
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36420d736885678-2">
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 f_col2_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1244378
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 12345
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 23456
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 34567
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 45678
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 56789
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 67890
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 78901
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 89012
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 90123
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901231
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901232
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901233
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36420d736885678-3">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36420d736885678-4">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select_type
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 table
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 type
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 possible_keys
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 key
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 key_len
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ref
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 rows
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Extra
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36420d736885678-5">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36420d736885678-6">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 SIMPLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 t_tb1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ref
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 uid_type_frid
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-v">
                 idx_corpid_qq1id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 uid_type_frid
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 8
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-m">
                 const
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1386
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Using
                </span>
                <span class="crayon-e">
                 index
                </span>
                <span class="crayon-v">
                 condition
                </span>
                <span class="crayon-sy">
                 ;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Using
                </span>
                <span class="crayon-v">
                 where
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36420d736885678-7">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
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                 +
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
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         </div>
        </div>
        <!-- [Format Time: 0.0392 seconds] -->
        <p>
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
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           <span class="crayon-language">
            Java
           </span>
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         </div>
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           共返回 1 行记录,花费 11.52 ms.
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          <table class="crayon-table">
           <tbody>
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               <div class="crayon-num" data-line="crayon-576869a364215794590558-1">
                1
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
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                共返回
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                行记录
                <span class="crayon-sy">
                 ,
                </span>
                花费
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 11.52
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ms
                </span>
                <span class="crayon-sy">
                 .
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0050 seconds] -->
        <p>
        </p>
        <p>
         t_tb1 表上有个索引
         <code>
          uid_type_frid(f_col2_id,f_type)
         </code>
         、
         <code>
          idx_corp_id_qq1id(f_col1_id,f_qq1_id)
         </code>
         ，而且如果选择后者时，f_qq1_id的过滤效果应该很佳，但却选择了前者。当使用 hint
         <code>
          use index(idx_corp_id_qq1id)
         </code>
         时：
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
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           <span class="crayon-language">
            Java
           </span>
          </div>
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         </div>
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           mysql&gt;explain extended SELECT f_col3_id,f_qq1_id FROM d_dbname.t_tb1  use index(idx_corpid_qq1id) WHERE f_col1_id=1226391 and f_col2_id=1244378 and f_qq1_id in (12345,23456,34567,45678,56789,67890,78901,89012,90123,901231,901232,901233);
+------+---------------+--------+--------+---------------------+------------------+------------+----------+-------------+------------------------------------+
| id   | select_type   | table  | type   | possible_keys       | key              | key_len    | ref      | rows        | Extra                              |
+------+---------------+--------+--------+---------------------+------------------+------------+----------+-------------+------------------------------------+
| 1    | SIMPLE        | t_tb1  | ref    | idx_corpid_qq1id    | idx_corpid_qq1id | 8          | const    | 2375752     | Using index condition; Using where |
+---- -+---------------+--------+--------+---------------------+------------------+------------+----------+-------------+------------------------------------+
共返回 1 行记录,花费 17.48 ms.

mysql&gt;show warnings;
+-----------------+----------------+-----------------------------------------------------------------------------------------------------------------------+
| Level           | Code           | Message                                                                                                               |
+-----------------+----------------+-----------------------------------------------------------------------------------------------------------------------+
| Warning         |           1739 | Cannot use range access on index 'idx_corpid_qq1id' due to type or collation conversion on field 'f_qq1_id'           |
| Note            |           1003 | /* select#1 */ select `d_dbname`.`t_tb1`.`f_col3_id` AS `f_col3_id`,`d_dbname`.`t_tb1`.`f_qq1_id` AS `f_qq1_id` from `d_dbname`.`t_tb1` USE INDEX (`idx_corpid_qq1id`) where |
|                 |                |  ((`d_dbname`.`t_tb1`.`f_col2_id` = 1244378) and (`d_dbname`.`t_tb1`.`f_col1_id` = 1226391) and (`d_dbname`.`t_tb1`.`f_qq1_id` in |
|                 |                | (12345,23456,34567,45678,56789,67890,78901,89012,90123,901231,901232,901233)))                                        |
+-----------------+----------------+-----------------------------------------------------------------------------------------------------------------------+
共返回 2 行记录,花费 10.81 ms.
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-2">
                2
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-3">
                3
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-4">
                4
               </div>
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                5
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-6">
                6
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-7">
                7
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-8">
                8
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-9">
                9
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-10">
                10
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-11">
                11
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-12">
                12
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-13">
                13
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-14">
                14
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-15">
                15
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-16">
                16
               </div>
               <div class="crayon-num" data-line="crayon-576869a36421b489971669-17">
                17
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36421b489971669-18">
                18
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a36421b489971669-1">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-e">
                 explain
                </span>
                <span class="crayon-e">
                 extended
                </span>
                <span class="crayon-e">
                 SELECT
                </span>
                <span class="crayon-v">
                 f_col3_id
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-e">
                 FROM
                </span>
                <span class="crayon-v">
                 d_dbname
                </span>
                <span class="crayon-sy">
                 .
                </span>
                <span class="crayon-e">
                 t_tb1
                </span>
                <span class="crayon-st">
                 use
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 index
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-v">
                 idx_corpid_qq1id
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 WHERE
                </span>
                <span class="crayon-v">
                 f_col1_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1226391
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 f_col2_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1244378
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 12345
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 23456
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 34567
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 45678
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 56789
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 67890
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 78901
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 89012
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 90123
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901231
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901232
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901233
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-2">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
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                </span>
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                </span>
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                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
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                </span>
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                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
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                 --
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                 --
                </span>
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36421b489971669-3">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select_type
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 table
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
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                </span>
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                 type
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                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
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                <span class="crayon-h">
                </span>
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                 possible_keys
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                <span class="crayon-h">
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                 |
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                </span>
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                 key
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                 |
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                </span>
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                 key_len
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                </span>
                <span class="crayon-o">
                 |
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                <span class="crayon-h">
                </span>
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                 ref
                </span>
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                </span>
                <span class="crayon-o">
                 |
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                <span class="crayon-h">
                </span>
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                 rows
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Extra
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-4">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
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                 --
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                 --
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                 --
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                 --
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                 --
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                 -
                </span>
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                 +
                </span>
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                 --
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                 --
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                 --
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                 --
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                 +
                </span>
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                 --
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                 --
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                <span class="crayon-o">
                 --
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                 --
                </span>
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                </span>
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                 --
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                 --
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                 --
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                 --
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                 --
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                 -
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                 --
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                 --
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                 --
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                 --
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                 --
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                 -
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                 --
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                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36421b489971669-5">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
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                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 SIMPLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 t_tb1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ref
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
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                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 idx_corpid_qq1id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 idx_corpid_qq1id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 8
                </span>
                <span class="crayon-h">
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                <span class="crayon-o">
                 |
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                </span>
                <span class="crayon-m">
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                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
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                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 2375752
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Using
                </span>
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                </span>
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                 Using
                </span>
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                </span>
                <span class="crayon-h">
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                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-6">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 -
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                 +
                </span>
                <span class="crayon-o">
                 --
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                 --
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                 --
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                 --
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                 --
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                 +
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                 --
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                 --
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                <span class="crayon-o">
                 --
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                 --
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                </span>
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                 --
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                <span class="crayon-o">
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                 --
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                <span class="crayon-o">
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                 --
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                 --
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                <span class="crayon-o">
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                 --
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                <span class="crayon-o">
                 -
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                <span class="crayon-o">
                 +
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                <span class="crayon-o">
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                <span class="crayon-o">
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                <span class="crayon-o">
                 --
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                 --
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                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36421b489971669-7">
                共返回
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                行记录
                <span class="crayon-sy">
                 ,
                </span>
                花费
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 17.48
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ms
                </span>
                <span class="crayon-sy">
                 .
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-8">
               </div>
               <div class="crayon-line" id="crayon-576869a36421b489971669-9">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-e">
                 show
                </span>
                <span class="crayon-v">
                 warnings
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-10">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                 --
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                 --
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                 --
                </span>
                <span class="crayon-o">
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                </span>
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
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                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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               <div class="crayon-line" id="crayon-576869a36421b489971669-11">
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                 |
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                 Level
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               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-12">
                <span class="crayon-o">
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               <div class="crayon-line" id="crayon-576869a36421b489971669-13">
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                 |
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               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-14">
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                </span>
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                </span>
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                </span>
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                <span class="crayon-o">
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               <div class="crayon-line" id="crayon-576869a36421b489971669-15">
                <span class="crayon-o">
                 |
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                </span>
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                </span>
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                </span>
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                 .
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                <span class="crayon-sy">
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                </span>
                <span class="crayon-v">
                 f_qq1_id
                </span>
                <span class="crayon-sy">
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                </span>
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                 in
                </span>
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                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-16">
                <span class="crayon-o">
                 |
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                 |
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                </span>
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                </span>
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                <span class="crayon-sy">
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                </span>
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                </span>
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                <span class="crayon-cn">
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                </span>
                <span class="crayon-sy">
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                <span class="crayon-cn">
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                </span>
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                </span>
                <span class="crayon-cn">
                 45678
                </span>
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                 ,
                </span>
                <span class="crayon-cn">
                 56789
                </span>
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                </span>
                <span class="crayon-cn">
                 67890
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 78901
                </span>
                <span class="crayon-sy">
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                <span class="crayon-cn">
                 89012
                </span>
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                </span>
                <span class="crayon-cn">
                 90123
                </span>
                <span class="crayon-sy">
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                </span>
                <span class="crayon-cn">
                 901231
                </span>
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                </span>
                <span class="crayon-cn">
                 901232
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-cn">
                 901233
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36421b489971669-17">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 -
                </span>
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                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 --
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                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36421b489971669-18">
                共返回
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 2
                </span>
                <span class="crayon-h">
                </span>
                行记录
                <span class="crayon-sy">
                 ,
                </span>
                花费
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 10.81
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ms
                </span>
                <span class="crayon-sy">
                 .
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.1028 seconds] -->
        <p>
        </p>
        <p>
         rows列达到200w行，但问题也发现了：select_type应该是 range 才对，key_len看出来只用到了
         <code>
          idx_corpid_qq1id
         </code>
         索引的第一列。上面explain使用了
         <code>
          extended
         </code>
         ，所以
         <code>
          show warnings;
         </code>
         可以很明确的看到 f_qq1_id 出现了隐式类型转换：f_qq1_id是varchar，而后面的比较值是整型。
        </p>
        <p>
         解决该问题就是避免出现隐式类型转换(implicit type conversion)带来的不可控：把f_qq1_id in的内容写成字符串：
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
        <div class="crayon-syntax crayon-theme-classic crayon-font-monaco crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover" id="crayon-576869a364224298251509" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
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           <span class="crayon-language">
            Java
           </span>
          </div>
         </div>
         <div class="crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
         </div>
         <div class="crayon-plain-wrap">
          <textarea class="crayon-plain print-no" data-settings="dblclick" readonly="" style="-moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; font-size: 12px !important; line-height: 15px !important;" wrap="soft">
           mysql&gt;explain SELECT f_col3_id,f_qq1_id FROM d_dbname.t_tb1 WHERE f_col1_id=1226391 and f_col2_id=1244378 and 
f_qq1_id in ('12345','23456','34567','45678','56789','67890','78901','89012','90123','901231');
+-------+---------------+--------+---------+--------------------------------+------------------+-------------+---------+---------+------------------------------------+
| id    | select_type   | table  | type    | possible_keys                  | key              | key_len     | ref     | rows    | Extra                              |
+-------+---------------+--------+---------+--------------------------------+------------------+-------------+---------+---------+------------------------------------+
| 1     | SIMPLE        | t_tb1  | range   | uid_type_frid,idx_corpid_qq1id | idx_corpid_qq1id | 70          |         | 40      | Using index condition; Using where |
+-------+---------------+--------+---------+--------------------------------+------------------+-------------+---------+---------+------------------------------------+
共返回 1 行记录,花费 12.41 ms.
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a364224298251509-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364224298251509-2">
                2
               </div>
               <div class="crayon-num" data-line="crayon-576869a364224298251509-3">
                3
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364224298251509-4">
                4
               </div>
               <div class="crayon-num" data-line="crayon-576869a364224298251509-5">
                5
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364224298251509-6">
                6
               </div>
               <div class="crayon-num" data-line="crayon-576869a364224298251509-7">
                7
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364224298251509-8">
                8
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a364224298251509-1">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-e">
                 explain
                </span>
                <span class="crayon-e">
                 SELECT
                </span>
                <span class="crayon-v">
                 f_col3_id
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-e">
                 FROM
                </span>
                <span class="crayon-v">
                 d_dbname
                </span>
                <span class="crayon-sy">
                 .
                </span>
                <span class="crayon-e">
                 t_tb1
                </span>
                <span class="crayon-e">
                 WHERE
                </span>
                <span class="crayon-v">
                 f_col1_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1226391
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 f_col2_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-cn">
                 1244378
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364224298251509-2">
                <span class="crayon-e">
                 f_qq1_id
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-s">
                 '12345'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '23456'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '34567'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '45678'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '56789'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '67890'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '78901'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '89012'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '90123'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-s">
                 '901231'
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364224298251509-3">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
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                 --
                </span>
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                 --
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                 --
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                 --
                </span>
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                 -
                </span>
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                 +
                </span>
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                 --
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                 --
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                 --
                </span>
                <span class="crayon-o">
                 +
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                 --
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                <span class="crayon-o">
                 --
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                 --
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                 --
                </span>
                <span class="crayon-o">
                 -
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                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
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                 --
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                <span class="crayon-o">
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
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                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
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                 --
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                <span class="crayon-o">
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                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364224298251509-4">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select_type
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 table
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 type
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 possible_keys
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 key
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 key_len
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ref
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 rows
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Extra
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364224298251509-5">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
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                <span class="crayon-o">
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                <span class="crayon-o">
                 --
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                 --
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                 --
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                 --
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                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 --
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                 --
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                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364224298251509-6">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 SIMPLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 t_tb1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 range
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 uid_type_frid
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-v">
                 idx_corpid_qq1id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 idx_corpid_qq1id
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 70
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 40
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Using
                </span>
                <span class="crayon-e">
                 index
                </span>
                <span class="crayon-v">
                 condition
                </span>
                <span class="crayon-sy">
                 ;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Using
                </span>
                <span class="crayon-v">
                 where
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364224298251509-7">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
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                 --
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                 --
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                 +
                </span>
                <span class="crayon-o">
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                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
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                 --
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                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
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                <span class="crayon-o">
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                 +
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                 --
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                <span class="crayon-o">
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                <span class="crayon-o">
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                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
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                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364224298251509-8">
                共返回
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                行记录
                <span class="crayon-sy">
                 ,
                </span>
                花费
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 12.41
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 ms
                </span>
                <span class="crayon-sy">
                 .
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0202 seconds] -->
        <p>
        </p>
        <p>
         扫描行数从1386减少为40。
        </p>
        <p>
         类似的还出现过一例：
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
        <div class="crayon-syntax crayon-theme-classic crayon-font-monaco crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover" id="crayon-576869a36422b480682463" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
         <div class="crayon-toolbar" data-settings=" mouseover overlay hide delay" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
          <span class="crayon-title">
          </span>
          <div class="crayon-tools" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
           <div class="crayon-button crayon-nums-button" title="切换是否显示行编号">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-plain-button" title="纯文本显示代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-wrap-button" title="切换自动换行">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-expand-button" title="点击展开代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-copy-button" title="复制代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <div class="crayon-button crayon-popup-button" title="在新窗口中显示代码">
            <div class="crayon-button-icon">
            </div>
           </div>
           <span class="crayon-language">
            Java
           </span>
          </div>
         </div>
         <div class="crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
         </div>
         <div class="crayon-plain-wrap">
          <textarea class="crayon-plain print-no" data-settings="dblclick" readonly="" style="-moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; font-size: 12px !important; line-height: 15px !important;" wrap="soft">
           SELECT count(0)  FROM d_dbname.t_tb2 where f_col1_id= '1931231'  AND f_phone in(098890);

| Warning | 1292 | Truncated incorrect DOUBLE value: '1512-98464356'
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a36422b480682463-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36422b480682463-2">
                2
               </div>
               <div class="crayon-num" data-line="crayon-576869a36422b480682463-3">
                3
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a36422b480682463-1">
                <span class="crayon-e">
                 SELECT
                </span>
                <span class="crayon-e">
                 count
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 0
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 FROM
                </span>
                <span class="crayon-v">
                 d_dbname
                </span>
                <span class="crayon-sy">
                 .
                </span>
                <span class="crayon-e">
                 t_tb2
                </span>
                <span class="crayon-e">
                 where
                </span>
                <span class="crayon-v">
                 f_col1_id
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '1931231'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 AND
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 f_phone
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 098890
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36422b480682463-2">
               </div>
               <div class="crayon-line" id="crayon-576869a36422b480682463-3">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Warning
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1292
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Truncated
                </span>
                <span class="crayon-e">
                 incorrect
                </span>
                <span class="crayon-t">
                 DOUBLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 value
                </span>
                <span class="crayon-o">
                 :
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '1512-98464356'
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0021 seconds] -->
        <p>
        </p>
        <p>
         优化后直接从扫描rows 100w行降为1。
        </p>
        <p>
         借这个机会，系统的来看一下mysql中的隐式类型转换。
        </p>
        <h2 id="articleHeader1">
         2. mysql隐式转换规则
        </h2>
        <h3 id="articleHeader2">
         2.1 规则
        </h3>
        <p>
         下面来分析一下
         <a href="http://dev.mysql.com/doc/refman/5.7/en/type-conversion.html" target="_blank">
          隐式转换的规则
         </a>
         ：
        </p>
        <blockquote>
         <ol>
          <li>
           两个参数至少有一个是 NULL 时，比较的结果也是 NULL，例外是使用 &lt;=&gt; 对两个 NULL 做比较时会返回 1，这两种情况都不需要做类型转换
          </li>
         </ol>
        </blockquote>
        <ol>
         <li>
          两个参数都是字符串，会按照字符串来比较，不做类型转换
         </li>
         <li>
          两个参数都是整数，按照整数来比较，不做类型转换
         </li>
         <li>
          十六进制的值和非数字做比较时，会被当做二进制串
         </li>
         <li>
          有一个参数是 TIMESTAMP 或 DATETIME，并且另外一个参数是常量，常量会被转换为 timestamp
         </li>
         <li>
          有一个参数是 decimal 类型，如果另外一个参数是 decimal 或者整数，会将整数转换为 decimal 后进行比较，如果另外一个参数是浮点数，则会把 decimal 转换为浮点数进行比较
         </li>
         <li>
          所有其他情况下，两个参数都会被转换为浮点数再进行比较
         </li>
        </ol>
        <p>
        </p>
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            Java
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           mysql&gt; select 11 + '11', 11 + 'aa', 'a1' + 'bb', 11 + '0.01a';  
+-----------+-----------+-------------+--------------+
| 11 + '11' | 11 + 'aa' | 'a1' + 'bb' | 11 + '0.01a' |
+-----------+-----------+-------------+--------------+
|        22 |        11 |           0 |        11.01 |
+-----------+-----------+-------------+--------------+
1 row in set, 4 warnings (0.00 sec)

mysql&gt; show warnings;
+---------+------+-------------------------------------------+
| Level   | Code | Message                                   |
+---------+------+-------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'aa'    |
| Warning | 1292 | Truncated incorrect DOUBLE value: 'a1'    |
| Warning | 1292 | Truncated incorrect DOUBLE value: 'bb'    |
| Warning | 1292 | Truncated incorrect DOUBLE value: '0.01a' |
+---------+------+-------------------------------------------+
4 rows in set (0.00 sec)


mysql&gt; select '11a' = 11, '11.0' = 11, '11.0' = '11', NULL = 1;
+------------+-------------+---------------+----------+
| '11a' = 11 | '11.0' = 11 | '11.0' = '11' | NULL = 1 |
+------------+-------------+---------------+----------+
|          1 |           1 |             0 |     NULL |
+------------+-------------+---------------+----------+
1 row in set, 1 warning (0.01 sec)
          </textarea>
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                <span class="crayon-v">
                 mysql
                </span>
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                 &gt;
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                 select
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                 11
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                 'aa'
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                 'bb'
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                 '0.01a'
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                 '11'
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                 'aa'
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                 'a1'
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                 'bb'
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                 '0.01a'
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               <div class="crayon-line" id="crayon-576869a364232108583127-9">
                <span class="crayon-v">
                 mysql
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                <span class="crayon-o">
                 &gt;
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                <span class="crayon-h">
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                 show
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                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-11">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Level
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Code
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Message
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-12">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-13">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Warning
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1292
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Truncated
                </span>
                <span class="crayon-e">
                 incorrect
                </span>
                <span class="crayon-t">
                 DOUBLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 value
                </span>
                <span class="crayon-o">
                 :
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 'aa'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-14">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Warning
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1292
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Truncated
                </span>
                <span class="crayon-e">
                 incorrect
                </span>
                <span class="crayon-t">
                 DOUBLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 value
                </span>
                <span class="crayon-o">
                 :
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 'a1'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-15">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Warning
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1292
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Truncated
                </span>
                <span class="crayon-e">
                 incorrect
                </span>
                <span class="crayon-t">
                 DOUBLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 value
                </span>
                <span class="crayon-o">
                 :
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 'bb'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-16">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Warning
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1292
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 Truncated
                </span>
                <span class="crayon-e">
                 incorrect
                </span>
                <span class="crayon-t">
                 DOUBLE
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 value
                </span>
                <span class="crayon-o">
                 :
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '0.01a'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-17">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-18">
                <span class="crayon-cn">
                 4
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 rows
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 set
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 0.00
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 sec
                </span>
                <span class="crayon-sy">
                 )
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-19">
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-20">
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-21">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-i">
                 select
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11a'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 11
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11.0'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 11
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11.0'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11'
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 NULL
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-22">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-23">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11a'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 11
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11.0'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 11
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11.0'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-s">
                 '11'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 NULL
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-24">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-25">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 0
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 NULL
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364232108583127-26">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a364232108583127-27">
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 row
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 set
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 warning
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 0.01
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 sec
                </span>
                <span class="crayon-sy">
                 )
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0198 seconds] -->
        <p>
        </p>
        <p>
         上面可以看出
         <code>
          11 + 'aa'
         </code>
         ，由于操作符两边的类型不一样且符合第g条，
         <code>
          aa
         </code>
         要被转换成浮点型小数，然而转换失败（字母被截断），可以认为转成了 0，整数
         <code>
          11
         </code>
         被转成浮点型还是它自己，所以
         <code>
          11 + 'aa' = 11
         </code>
         。
        </p>
        <p>
         <code>
          0.01a
         </code>
         转成double型也是被截断成
         <code>
          0.01
         </code>
         ，所以
         <code>
          11 + '0.01a' = 11.01
         </code>
         。
        </p>
        <p>
         等式比较也说明了这一点，
         <code>
          '11a'
         </code>
         和
         <code>
          '11.0'
         </code>
         转换后都等于
         <code>
          11
         </code>
         ，这也正是文章开头实例为什么没走索引的原因： varchar型的f_qq1_id，转换成浮点型比较时，等于 12345 的情况有无数种如12345a、12345.b等待，MySQL优化器无法确定索引是否更有效，所以选择了其它方案。
        </p>
        <p>
         但并不是只要出现隐式类型转换，就会引起上面类似的性能问题，最终是要看转换后能否有效选择索引。像
         <code>
          f_id = '654321'
         </code>
         、
         <code>
          f_mtime between '2016-05-01 00:00:00' and '2016-05-04 23:59:59'
         </code>
         就不会影响索引选择，因为前者f_id是整型，即使与后面的字符串型数字转换成double比较，依然能根据double确定f_id的值，索引依然有效。后者是因为符合第e条，只是右边的常量做了转换。
        </p>
        <p>
         开发人员可能都只要存在这么一个隐式类型转换的坑，但却又经常不注意，所以干脆无需记住那么多规则，该什么类型就与什么类型比较。
        </p>
        <h3 id="articleHeader3">
         2.2 隐式类型转换的安全问题
        </h3>
        <p>
         implicit type conversion 不仅可能引起性能问题，还有可能产生安全问题。
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
        <div class="crayon-syntax crayon-theme-classic crayon-font-monaco crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover" id="crayon-576869a36423b485787590" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
         <div class="crayon-toolbar" data-settings=" mouseover overlay hide delay" style="font-size: 12px !important;height: 18px !important; line-height: 18px !important;">
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           <div class="crayon-button crayon-expand-button" title="点击展开代码">
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           </div>
           <span class="crayon-language">
            Java
           </span>
          </div>
         </div>
         <div class="crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
         </div>
         <div class="crayon-plain-wrap">
          <textarea class="crayon-plain print-no" data-settings="dblclick" readonly="" style="-moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; font-size: 12px !important; line-height: 15px !important;" wrap="soft">
           mysql&gt; desc t_account;
+-----------+-------------+------+-----+---------+----------------+
| Field     | Type        | Null | Key | Default | Extra          |
+-----------+-------------+------+-----+---------+----------------+
| fid       | int(11)     | NO   | PRI | NULL    | auto_increment |
| fname     | varchar(20) | YES  |     | NULL    |                |
| fpassword | varchar(50) | YES  |     | NULL    |                |
+-----------+-------------+------+-----+---------+----------------+

mysql&gt; select * from t_account;
+-----+-----------+-------------+
| fid | fname     | fpassword   |
+-----+-----------+-------------+
|   1 | xiaoming  | p_xiaoming  |
|   2 | xiaoming1 | p_xiaoming1 |
+-----+-----------+-------------+

假如应用前端没有WAF防护，那么下面的sql很容易注入：
mysql&gt; select * from t_account where fname='A' ;

fname传入  A' OR 1='1  

mysql&gt; select * from t_account where fname='A' OR 1='1';
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-2">
                2
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-3">
                3
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-4">
                4
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-5">
                5
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-6">
                6
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-7">
                7
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-8">
                8
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-9">
                9
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-10">
                10
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-11">
                11
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-12">
                12
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-13">
                13
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-14">
                14
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-15">
                15
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-16">
                16
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-17">
                17
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-18">
                18
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-19">
                19
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-20">
                20
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-21">
                21
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a36423b485787590-22">
                22
               </div>
               <div class="crayon-num" data-line="crayon-576869a36423b485787590-23">
                23
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a36423b485787590-1">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 desc
                </span>
                <span class="crayon-v">
                 t_account
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-2">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-3">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Field
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Type
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 Null
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Key
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 Default
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 Extra
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-4">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-5">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fid
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 int
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 11
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 NO
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 PRI
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 NULL
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 auto_increment
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-6">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fname
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 varchar
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 20
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 YES
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 NULL
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-7">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fpassword
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 varchar
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 50
                </span>
                <span class="crayon-sy">
                 )
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 YES
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-t">
                 NULL
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-8">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-9">
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-10">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 *
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 from
                </span>
                <span class="crayon-v">
                 t_account
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-11">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-12">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fid
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fname
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fpassword
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-13">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-14">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 xiaoming
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 p_xiaoming
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-15">
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 2
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 xiaoming1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 p_xiaoming1
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 |
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-16">
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 --
                </span>
                <span class="crayon-o">
                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-17">
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-18">
                假如应用前端没有
                <span class="crayon-i">
                 WAF
                </span>
                防护，那么下面的
                <span class="crayon-i">
                 sql
                </span>
                很容易注入：
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-19">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 *
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 from
                </span>
                <span class="crayon-e">
                 t_account
                </span>
                <span class="crayon-e">
                 where
                </span>
                <span class="crayon-v">
                 fname
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-s">
                 'A'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-20">
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-21">
                <span class="crayon-i">
                 fname
                </span>
                传入
                <span class="crayon-h">
                </span>
                <span class="crayon-i">
                 A
                </span>
                <span class="crayon-s">
                 ' OR 1='
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-h">
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a36423b485787590-22">
               </div>
               <div class="crayon-line" id="crayon-576869a36423b485787590-23">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 *
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 from
                </span>
                <span class="crayon-e">
                 t_account
                </span>
                <span class="crayon-e">
                 where
                </span>
                <span class="crayon-v">
                 fname
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-s">
                 'A'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 OR
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 1
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-s">
                 '1'
                </span>
                <span class="crayon-sy">
                 ;
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0134 seconds] -->
        <p>
        </p>
        <p>
         攻击者更聪明一点： fname传入
         <code>
          A'+'B
         </code>
         ，fpassword传入
         <code>
          ccc'+0
         </code>
         ：
        </p>
        <!-- Crayon Syntax Highlighter v_2.7.2_beta -->
        <div class="crayon-syntax crayon-theme-classic crayon-font-monaco crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover" id="crayon-576869a364242628147841" style=" margin-top: 12px; margin-bottom: 12px; font-size: 12px !important; line-height: 15px !important;">
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            <div class="crayon-button-icon">
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            <div class="crayon-button-icon">
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           <div class="crayon-button crayon-expand-button" title="点击展开代码">
            <div class="crayon-button-icon">
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           <div class="crayon-button crayon-popup-button" title="在新窗口中显示代码">
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           </div>
           <span class="crayon-language">
            Java
           </span>
          </div>
         </div>
         <div class="crayon-info" style="min-height: 16.8px !important; line-height: 16.8px !important;">
         </div>
         <div class="crayon-plain-wrap">
          <textarea class="crayon-plain print-no" data-settings="dblclick" readonly="" style="-moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4; font-size: 12px !important; line-height: 15px !important;" wrap="soft">
           mysql&gt; select * from t_account where fname='A'+'B' and fpassword='ccc'+0;
+-----+-----------+-------------+
| fid | fname     | fpassword   |
+-----+-----------+-------------+
|   1 | xiaoming  | p_xiaoming  |
|   2 | xiaoming1 | p_xiaoming1 |
+-----+-----------+-------------+
2 rows in set, 7 warnings (0.00 sec)
          </textarea>
         </div>
         <div class="crayon-main" style="">
          <table class="crayon-table">
           <tbody>
            <tr class="crayon-row">
             <td class="crayon-nums " data-settings="show">
              <div class="crayon-nums-content" style="font-size: 12px !important; line-height: 15px !important;">
               <div class="crayon-num" data-line="crayon-576869a364242628147841-1">
                1
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364242628147841-2">
                2
               </div>
               <div class="crayon-num" data-line="crayon-576869a364242628147841-3">
                3
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364242628147841-4">
                4
               </div>
               <div class="crayon-num" data-line="crayon-576869a364242628147841-5">
                5
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364242628147841-6">
                6
               </div>
               <div class="crayon-num" data-line="crayon-576869a364242628147841-7">
                7
               </div>
               <div class="crayon-num crayon-striped-num" data-line="crayon-576869a364242628147841-8">
                8
               </div>
              </div>
             </td>
             <td class="crayon-code">
              <div class="crayon-pre" style="font-size: 12px !important; line-height: 15px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;">
               <div class="crayon-line" id="crayon-576869a364242628147841-1">
                <span class="crayon-v">
                 mysql
                </span>
                <span class="crayon-o">
                 &gt;
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 select
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-o">
                 *
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 from
                </span>
                <span class="crayon-e">
                 t_account
                </span>
                <span class="crayon-e">
                 where
                </span>
                <span class="crayon-v">
                 fname
                </span>
                <span class="crayon-o">
                 =
                </span>
                <span class="crayon-s">
                 'A'
                </span>
                <span class="crayon-o">
                 +
                </span>
                <span class="crayon-s">
                 'B'
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-st">
                 and
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 fpassword
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                 --
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                 --
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                 -
                </span>
                <span class="crayon-o">
                 +
                </span>
               </div>
               <div class="crayon-line crayon-striped-line" id="crayon-576869a364242628147841-8">
                <span class="crayon-cn">
                 2
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 rows
                </span>
                <span class="crayon-st">
                 in
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-v">
                 set
                </span>
                <span class="crayon-sy">
                 ,
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-cn">
                 7
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-e">
                 warnings
                </span>
                <span class="crayon-h">
                </span>
                <span class="crayon-sy">
                 (
                </span>
                <span class="crayon-cn">
                 0.00
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                 sec
                </span>
                <span class="crayon-sy">
                 )
                </span>
               </div>
              </div>
             </td>
            </tr>
           </tbody>
          </table>
         </div>
        </div>
        <!-- [Format Time: 0.0050 seconds] -->
        <p>
        </p>
        <h2 id="articleHeader4">
         参考
        </h2>
        <ul>
         <li>
          <a href="https://yq.aliyun.com/articles/39477" target="_blank">
           MySQL隐式转化整理
          </a>
         </li>
         <li>
          <a href="http://blog.itpub.net/22418990/viewspace-1302080/" target="_blank">
           WHRER条件里的数据类型必须和字段数据类型一致
          </a>
         </li>
         <li>
          <a href="https://vagosec.org/2013/04/mysql-implicit-type-conversion/" target="_blank">
           Implicit type conversion in MySQL
          </a>
         </li>
        </ul>
        <hr/>
        <p>
         原文链接地址：
         <a href="http://seanlook.com/2016/05/05/mysql-type-conversion/" target="_blank">
          http://seanlook.com/2016/05/05/mysql-type-conversion/
         </a>
        </p>
        <hr/>
       </div>
       <div class="clearfix mt10">
        <ul class="article-operation list-inline pull-left">
         <li>
          <a class="text-muted" href="https://segmentfault.com/a/1190000005136982">
           5月16日发布
          </a>
         </li>
        </ul>
       </div>
      </div>
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